Hydraulic transmission of energy has lately been receiving increasing attention in the agricultural and construction equipment fields, because of its ease of operation and the possibility for its stepless change of torque and speed, especially where large forces are involved. This applies to such operations as lifting, digging, shoveling and the like, but this type of transmission is also extensively used in the propulsion of heavy vehicles, notably tracked vehicles, agricultural tractors, and earth-moving machinery.
Present methods of hydraulic transmissions comprise an engine-driven fixed or variable displacement pump and one or more fixed or variable displacement motors, interconnected by piping and valve means. The efficiency of these transmissions is relatively low on account of the friction losses incurred by the conversion of the reciprocating motion of the pistons into rotary motion by means of piston rods and crankshafts, and by the re-conversion of this rotary motion into reciprocating motion of the pump pistons through a swashplate or other means. The liquid pressure energy is eventually converted into mechanical energy by means of a linear actuator or a rotary motor, dependent on the kind and direction of movement required.